Electrical performance and oxygen relaxation behaviour in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds were investigated. The oxide ion conductivity of Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds increased first and then decreased with increasing Mg-doped content. The highest oxide ion conductivity of 4.7 × 10 −3 S cm −1 at 773 K was observed for the Na 0.5 Bi 0.5 Ti 0.96 Mg 0.04 O 2.96 compound. A typical relaxation peak in the Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x samples was observed. The activation energy and pre-exponential factors were determined as (1.0 eV, 4.7 × 10 −16 s) and (0.94−1.0 eV, 6.8 × 10 −14 −3.1 × 10 −13 s) from internal friction and dielectric relaxation measurement, respectively. The lower oxide ion conductivity in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x (x = 0.06, 0.08, 0.10) compounds may arise from the lower vacancy mobility. Judging from the electrical performance and relaxation parameters, although lower-level Mgdoping can improve oxide ionic conductor, oxygen vacancy mobility in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds cannot be improved with increasing Mg-doping content. These results will be meaningful to ameliorate the electrical properties of Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds and understand the relationship between the electrical properties and structure.
Two kinds of unidirectional laminates made from carbon/epoxy composite named M40/DFA-1 & M40/DFA-N3(nano TiO2 contained) are selected to study the different effects between different test sequences of atomic oxygen/thermal cycling. Based on the ground simulating test of atomic oxygen and thermal cycling, several kinds of tests and analysis are conducted, such as surface morphology observation, mass loss test, inter-laminar shear strength test, and X-ray photoelectron analysis of surface components. After the exposure of atomic oxygen and thermal cycling, surface erosions is observed on both of the materials, in addition, mechanical properties are both changed. It must be highlight that, under the condition of 1.5×1020 atoms/cm2 AO and 200 thermal cycles within the range of -150°C∼+150°C, different sequences lead to different results, either the extend or the tendency. In which, samples under AO+TC sequence exhibited relatively higher mass loss and erosion rate as well as more severe mechanical performance degradation.
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